Abstract

The ionizationenergy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for CoC and CoC+ are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ/CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, 1Σ+, for the ground state of CoC+. The CCSDTQ/CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ωe (ωe+) = 956 (992) and 976 (1004) cm−1 and the bond lengths re (re+) = 1.560 (1.528) and 1.550 (1.522) Å, respectively, for CoC (CoC+) in comparison with the experimental values. The CCSDTQ/CBS calculations give the prediction of D0(Co+–C) − D0(Co–C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC/CoC+. For the experimental D0 and ΔHof0 values of CoC/CoC+, which are not known experimentally, we recommend the following CCSDTQ/CBS predictions: ΔHof0(CoC) = 775.7 kJ/mol and ΔHof0(CoC+) = 1522.5 kJ/mol, ΔHof298(CoC) = 779.2 kJ/mol and ΔHo298(CoC+) = 1526.0 kJ/mol.

Received 09 December 2012Accepted 06 February 2013Published online 01 March 2013

Acknowledgments:

The theoretical work described in this article was fully supported by a Strategic Research Grant from City University of Hong Kong (Project No. 7002616). C.Y.N. was supported by the National Science Foundation (NSF) Chemical Structures, Dynamics, and Mechanisms Program Grant No. CHE 0910488.

Article outline:I. INTRODUCTIONII. THEORETICAL METHODSIII. RESULTS AND DISCUSSIONA. Equilibrium bond length and harmonic vibration frequency of CoC and CoC+B. Ionizationenergies of CoC and CoC. Dissociation energies of the CoC and CoC+D. Heats of formation for CoC and CoC+IV. CONCLUSIONS